1. Field of the Invention
The present invention relates to a display device having a display screen which is formed on a flat plate surface by using a light emitting element typified by an electro luminescence element, and more particularly relates to an electronic apparatus using the display device.
2. Description of Related Art
In recent years, with the development in communication technologies, portable telephone sets have been widely used. In future, transmission of moving pictures and transmission of a large volume of information are expected. On the other hand, through reduction in weight of personal computers (PCs), those adapted for mobile communication have been produced. Information terminals called PDA originated in electronic notebooks have also been produced in large quantities and widely used. In addition, with the advance of display devices, most of those portable information apparatuses are equipped with a flat panel display.
Among active matrix display devices, manufacturing of a display device by the use of low temperature poly-silicon thin film transistors (referred to as TFTs hereinafter) is promoted. The use of low temperature poly-silicon TFTs has advantages in that in addition to manufacturing of a pixel, a signal line driver circuit can be integrally formed around a pixel portion in a display device. Thus, it is possible to realize miniaturization and high definition of a display device, and such a display device is expected to be more widely used in future.
For portable PCs, tablet PCs have been developed. As shown in FIGS. 2A and 2B, a tablet PC comprises a first housing 201, a second housing 202, a keyboard 203, a touch pad 204, a display portion 205 including a touch sensor, an axis of rotation 206, and a touch pen 207. When using the keyboard 203 in such a tablet PC, as shown in FIG. 2A, data can be input with the keyboard 203 while looking at the display as in other notebook PCs. Meanwhile, when characters and data are input without using the keyboard 203, as shown in FIG. 2B, the display portion 205 including a touch sensor and the touch pen 207 are used by rotating the first housing 201 in a complicated way and covering the keyboard 203 with the first housing 201.
As for portable telephone sets, bar-type phones have been replaced by flip phones, and among flip phones, those having two displays have been actively developed. FIGS. 3A, 3B and 3C show an internal side, an external side and a lateral side of a flip phone, respectively. The flip phone shown in FIGS. 3A to 3C comprises a first housing 301, a second housing 302, a first display portion 303, a second display portion 304, a speaker 306, an antenna 307, a hinge 308, a keyboard 309, a microphone 310, and a battery 311. As shown in FIGS. 3A to 3C, a sub-display (the second display portion 304) is provided as well as a main display (the first display portion 303), and thus the time, a battery charge status, a message reception status and the like can be displayed on the sub-display instead of on the main display (see Japanese Laid-Open Patent Application No. 2001-285445, for example).